When a motor vehicle is subjected to the crosswind during running at high speed, a vehicle body may be carried away to the leeward or the running may become unsteady due to the correcting control by steering against the crosswind.
Furthermore, when the motor vehicle tries to outrun a plurality of large-sized vehicles on the leeward against the crosswind, the motor vehicle is intermittently subjected to the crosswind, whereby, above-described unsteadiness of the running may be caused, and it becomes necessary to perform steering control to correct the running against the unsteadiness.
As means for improving the control stabiltiy of the motor vehicle during running at high speed against the aforesaid crosswind, there is a method of improving the chassis (suspension and tires) or the characteristics of aerodynamics of the body (particularly, decreases in the yawing moment coefficient CY and the lift coefficient CL).
The above-described yawing moment coefficient CY is a coefficient of moment for rotating the vehicle in the lateral direction, and generated when the vehicle is subjected to the crosswind, i.e., the running wind has an yaw angle .psi. to the vertical center surface in the longitudinal direction of the vehicle.
This will hereunder be described in detail. As shown in FIG. 11, when a motor vehicle 1 is subjected to the crosswind and the yaw angle .psi. of a running wind 2 becomes .psi. .noteq. 0, a running wind 2 is divided at left corner portion 3 of a front side of the motor vehicle 1 into two air streams including an air stream flowing along the left side surface of the motor vehicle 1 and another air stream flowing along the front surface and to the right side surface of the motor vehicle 1.
At this time, there occurs a difference in flow velocity between these divided air streams, and a difference in pressure distribution around the vehicle body of the motor vehicle 1 is generated due to the difference in flow velocity as shown in FIG. 11.
As apparent from this drawing, in general, positive pressure is generated at the left side surface on the windward side of the motor vehicle 1 and negative pressure is generated at the right side surface on the leeward side.
Consequently, due to this difference in pressure, a moment for rotating the motor vehicle 1 to the right in the drawing is generated to the motor vehicle, and this coefficient is the above-described yawing moment coefficent CY.
Here, the relationship between the yaw angle .psi. and the yawing moment coefficient CY differs depending on the configuration of the vehicle body, however, in general, CY has the maximum value in the proximity of .psi.=25.degree..
The characteristics of CY as described above is mainly due to change in pressure (change in flow velocity) on the leeward side, i.e., in the right side corner portion of the motor vehicle 1 in the drawing.
More specifically, on the leeward side in the right corner portion 4 of the front side, the air stream flows along the outer surface of the vehicle body, and, even when the air stream is separated, the air stream is immediately attached again, so that the flow velocity is high and the negative pressure is high.
When the yaw angle reaches a certain value (in general, 25.degree.-30.degree.) or thereabove, the air stream is separated the outer surface of the vehicle body in the corner portion of the front side, whereby the negative pressure is lowered as compared with that when the air stream flows along the outer surface of the vehicle body.
Consequently, it is known that, when this corner portion is made angular or the radius of curvature thereof is decreased, separation of the air stream occurs and the yawing moment coefficient CY is reduced.
Now, regarding the relationship between the yawing moment coefficient CY and the drag coefficient CD, when the radius of curvature of the corner portion of the front side of the motor vehicle is decreased to reduce the yawing moment coefficent CY, the drag coefficient CD becomes high, whereby such a problem is presented that an adverse influence such as increased fuel consumption and the like is caused.
To obviate this problem, in Japanese Utility Model Application No. 188900/1983, the present application proposed a construction of front side portions of a motor vehicle, wherein turbulent fins forwardly protruded from a vehicle body are secured to a branching position where the running wind from the directly forward direction of the vehicle body is divided into the upward and the lateral directions in a front side corner portion of the vehicle body.
The above-described construction of the front side portion of the motor vehicle presents the problem that the yawing moment coefficient CY can be decreased without increasing the drag coefficient CD, however, the turbulent fins become large-sized.
To obviate this problem, further, in Japanese Utility Model Application Nos. 79241/1984 and 134037/1984, the present applicant proposed a construction of a front side portions of a motor vehicle, wherein the construction is compact in size, and the yawing moment coefficient CY can be decreased without increasing the drag coefficient CD.
However, in all of the above-described construction of the front side portions, the turbulent fins are protruded from the front side portions, whereby the appearance of the vehicle is lowered, and, there is such a problem that, when the yaw angle is larger than a certain degree, the effect of decreasing the yawing moment coefficient CY is high, and, when the yaw angle is small, improvements are limited.
Similar problems are presented on the rear side portions of the motor vehicle as will be described hereunder.
In recent years, in some of the three-box cars and fastback cars, in order to reduce the drag coefficient CD and to decrease the air resistance FD during running, the shape of a rear quarter portion from a quarter pillar to a rear window is stream-lined, in which the radius of curvature is made large.
However, in the vehicles, wherein the shape of the rear quarter portion is stream-lined by increasing the radius of curvature, the drag coefficient CD can be decreased, on the contrary, there is such a problem that the yawing moment coefficient CY is increased.
In contrast thereto, such vehicles have been commercialized that fins are secured to the rear quarter portions, and air stream flowing along the rear quarter portions are actively separated from the surface of the rear quarter portions by use of the fins.
Furthermore, in order to decrease the yawing moment coefficient CY, the present applicant proposed a vehicle, in Japanese Utility Model Kokai (Laid-Open) No. 143985/1982, wherein movable fins which are each selectively, positionally adjustable to a stored position within a compartment and a protruded position from a compartment, are provided at the right and left rear quarter portions of the vehicle.
However, such a problem is presented that, when the fins are secured to the rear quarter portions to decrease the yawing moment coefficient CY, the fins are formed protrudingly from the rear quarter portions, the drag coefficient CD cannot be made further smaller. Particularly, in the vehicles, wherein body surface is flushed, it is not preferably to protrude the fins from the rear quarter portions.
Furthermore, the vehicle proposed in the aforesaid Utility Model Kokai (Laid-Open) No. 143985/1982 presents the problem that the fins are made movable, whereby the arrangement becomes complicated.
The present invention has as its object the provision of a construction of side corner portions of a motor vehicle, wherein the yawing moment coefficient CY can be decreased without providing protruding vehicles such as a turbulent fins on the side corner portions and increasing the drag coefficient CD.